In the manufacture of wire the thickness of the insulation or other coating surrounding the conductive wire must meet certain requirements or standards such as those set by the Underwriters Laboratories. In the past, methods for coating the outer surface of wire have included extrusion of polymeric materials including nylon and thermoplastics such as polyvinyl chloride (PVC) thereon. However, the extrusion devices utilized have typically been disadvantageously limited in the accuracy and uniformity with which the coating material is extruded onto the surface of the wire. Due to these limitations, it has been necessary to place a greater amount of coating material onto the outer surface of the wire than required by the applicable standards.
For example, if the particular standard requires an insulation thickness of ten thousandths of an inch (0.01 inches) and the accuracy of the extrusion device or extrusion head is only five thousandths of an inch (0.005 inches) then the extrusion device must be configured to extrude an insulating material coating of at least fifteen thousandths of an inch (0.015 inches) in order to assure that the thickness of the insulation of the conductive wire would meet the 0.01 inch standard. Thus, in many cases the actual thickness of the coatings on wire have been greater than required by the applicable standards. In manufacturing terms, the cost of the additional coating material placed on the wire adds up quickly, particularly with respect to the manufacture of wire wherein the speed of the extrusion process, or speed at which such wire is insulated, may far exceed one thousand feet of wire per minute. The cost of the additional coating material can be significant. This background also applies to the extruding of a nylon jacket onto insulated wire.
Further, in known devices for extruding coating material onto conductive wire, additional manufacturing costs are incurred when the extrusion process must be stopped in order to clean the extrusion device or extrusion head. In such known devices the extrusion process can be hindered when the coating material burns within the extrusion head. When such burning occurs, the extrusion process must be stopped so that the extrusion head can be removed and cleaned of all burned material.
Accordingly, it is desirable and advantageous to provide a device for more accurately extruding coating material onto the outer surface of wire in order to reduce material costs. It also is desirable and advantageous to provide a device for extruding coating material onto the outer surface of wire wherein the device requires less cleaning thereby reducing the down time of the extrusion process.